WO2008055356A1

WO2008055356A1 - Bus bar assembly for an electrochemical cell stack

Info

Publication number: WO2008055356A1
Application number: PCT/CA2007/002018
Authority: WO
Inventors: Nathaniel Ian Joos; Mario Dzamarija
Original assignee: Hydrogenics Corporation
Priority date: 2006-11-10
Filing date: 2007-11-09
Publication date: 2008-05-15

Abstract

A bus bar for an electrochemical cell stack and an electrochemical cell stack are disclosed. The bus bar has an extended tab portion with at least one mounting hole, and a fastening block with at least one threaded hole corresponding to the at least one mounting hole of the tab portion. The tab portion may include an angled portion, with the at least one mounting hole arranged on the angled portion. The bus bar may be seated in an insulator plate having an extended tab portion corresponding to the tab portion of the bus bar. The fastening block may have threaded inserts forming the threaded holes or they may be formed directly in the fastening block.

Description

TITLE: BUS BAR ASSEMBLY FOR AN ELECTROCHEMICAL CELL

STACK

PRIORITY

[0001] This application claims the benefit of United States Provisional

Application No. 60/865,297, filed November 10, 2006.

FIELD [0002] This invention relates to an arrangement for a bus bar for an electrochemical cell stack, and more particularly relates to a terminal attachment means for the bus bar.

BACKGROUND

[0003] The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.

[0004] Fuel cells have been proposed as a clean, efficient and environmentally friendly source of power that can be utilized for various applications. A fuel cell is an electrochemical device that produces an electromotive force by bringing the fuel (typically hydrogen) and an oxidant (typically air) into contact with two suitable electrodes and an electrolyte. A fuel, such as hydrogen gas, for example, is introduced at a first electrode (anode) where it reacts electrochemically in the presence of the electrolyte to produce electrons and cations. The electrons are conducted from the anode to a second electrode (cathode) through an electrical circuit connected between the electrodes. Cations pass through the electrolyte to the cathode. Simultaneously, an oxidant, such as oxygen gas or air is introduced to the cathode where the oxidant reacts electrochemically in presence of the electrolyte and catalyst, producing anions and consuming the electrons circulated through the electrical circuit; the cations are consumed at the cathode. The anions formed at the cathode react with the cations to form a reaction product. The anode may alternatively be referred to as a fuel or oxidizing electrode and the cathode may alternatively be referred to as an oxidant or reducing electrode. The half-cell reactions at the two electrodes are, respectively, as follows:

H₂ → 2H⁺ + 2e- (1)

[0005] The external electrical circuit withdraws electrical current and thus receives electrical power from the fuel cell. The overall fuel cell reaction produces electrical energy as shown by the sum of the separate half-cell reactions written above. Water and heat are typical by-products of the reaction. Accordingly, the use of fuel cells in power generation offers potential environmental benefits compared with power generation from combustion of fossil fuels or by nuclear activity. Some examples of applications are distributed residential power generation and automotive power systems to reduce emission levels.

[0006] In practice, fuel cells are not operated as single units. Rather, fuel cells are connected in series, stacked one on top of the other, or placed side by side. A series of fuel cells, referred to as fuel cell stack, is normally enclosed in a housing. The fuel and oxidant are directed through manifolds to the electrodes, while cooling is provided either by the reactants or by a separate cooling medium. Also within the stack are current collectors, cell-to- cell seals and insulation. Piping and various instruments are externally connected to the fuel cell stack for supplying and controlling the fluid streams in the system. The stack, housing, and associated hardware make up the fuel cell unit.

[0007] There are various known types of fuel cells. For example, proton exchange membrane (PEM) fuel cells are one of the most promising replacements for traditional power generation systems, as a PEM fuel cell enables a simple, compact fuel cell to be designed, which is robust and which can be operated at temperatures not too different from ambient temperatures. Usually, PEM fuel cells are fuelled by pure hydrogen gas, as it is electrochemically reactive and the by-products of the reaction are water and heat, which is environmentally friendly. A conventional PEM fuel cell usually comprises two flow filed plates (bipolar plates), namely, an anode flow field plate and a cathode flow field plate, with a proton exchange membrane (MEA) disposed there between. The MEA includes the actual proton exchange membrane and layers of catalyst for fuel cell reaction coated onto the membrane. Additionally, a gas diffusion media (GDM) or gas diffusion layer (GDL) is provided between each flow field plate and the PEM. The GDM or GDL facilitates the diffusion of the reactant gas, either the fuel or oxidant, to the catalyst surface of the MEA while provides electrical conductivity between each flow field plate and the PEM.

[0008] Each flow field plate typically has three apertures or openings at each end, each aperture representing either an inlet or outlet for one of fuel, oxidant and coolant. However, it is possible to have multiple inlets and outlets on flow field plates for each reactant gas or coolant, depending on the fuel cell or stack design. When a fuel cell stacked in assembled, the anode flow field plate of one cell abuts against the cathode flow field plate of an adjacent cell. These apertures extend throughout the thickness of the flow field plates and align to form elongate distribution channels extending perpendicular to the flow field plates and through the entire fuel cell stack when the flow field plates stack together to form a complete fuel cell stack. A flow field usually comprises at least one, and in most cases a plurality of, open-faced flow channels that fluidly communicate (connect) appropriate inlet and outlet. As a reactant gas flows through the channels, it diffuses through GDM and reacts on the MEA in the presence of catalyst. A continuous flow through ensures that, while most of the fuel or oxidant is consumed, any contaminant are continually flushed through the fuel cell. The flow field may be provided on either face or both faces of the flow field plate. Typically, fuel or oxidant flow fields are formed respectively on the face of the anode and cathode flow field plate that faces toward the MEA (hereinafter, referred to as "front face"). A coolant flow field may be provided on either the face of either of anode or cathode flow field plate that faces away from the MEA (hereinafter, referred to as "rear face").

[0009] When a complete fuel cell stack is formed, a pair of current collector plates (bus bars) are provided immediately adjacent the outmost flow field plates (starter plates), one on each side of the stack, to collect current from the fuel cell stack and supply the current to an external electrical circuit. A pair of insulator plates is provided immediately outside of the current collector plates and a pair of end plates is located immediately adjacent insulator. Alternatively, an end plate may be utilized, which has an electrically insulating coating on the surfaces that are accessible to the outside when the stack is assembled. A seal is provided between each pair of adjacent plates. The seal is usually in the form of gaskets made of resilient materials that are compatible with the fuel cell environment. A fuel cell stack, after assembly, is commonly clamped to secure the elements and ensure that adequate compression is applied to the seals and active areas of the fuel cell stack. This method ensures that the contact resistance is minimized and the electrical resistance of the cells is at a minimum.

[0010] For the purposes of this patent application, the term "insulator end plate" is used to describe either a first alternative having a combination of an insulator plate and electrically conducting end plate, or a second alternative having an end plate with an outer electrically insulating layer except on the side of the end plate making contact with the bus bar.

[0011] The bus bar may be arranged in a recess or pocket provided in the insulator plate, for the first alternative of an insulator end plate, or in the end plate itself, for the second alternative.

[0012] It can be appreciated from the previous discussion that a problem in conventional fuel cell is that the bus bar needs to be electrically conductively connected to the outside of the electrochemical stack (fuel cell stack or electrolyzer stack). Traditionally, this has been accomplished by utilizing a metallic terminal block fixedly attached to a tab of the bus bar, most often using screws threaded into the terminal block. The tab itself cannot be threaded and used as an attachment point for the connector screws because the bus bar is generally not thick enough to provide a sufficient number of threads for a mechanically sound connection. The traditional terminal block adds weight to the system and occupies a significant space (volume) between the bus bars of a stack. This is especially problematic for small stacks, i.e. stacks having few electrochemical cells.

SUMMARY

[0013] The following introduction is intended to introduce the reader to this specification but not to define any invention. One or more inventions may reside in a combination or sub-combination of the apparatus elements or method steps described below or in other parts of this document. The inventor(s) does not waive or disclaim his rights to any invention or inventions disclosed in this specification merely by not describing such other invention or inventions in the claims.

[0014] In accordance with one aspect of the invention, there is provided an electrochemical cell stack comprising: a bus bar having a tab portion, the tab portion having at least one mounting hole; and a fastening block having at least one threaded hole corresponding to the at least one mounting hole of the tab portion.

[0015] In a particular embodiment of the electrochemical cell stack, the tab portion of the bus bar comprises an angled portion. The at least one mounting hole may be arranged on the angled portion. The angled portion may be generally perpendicular to a general plane of the bus bar.

[0016] The electrochemical cell stack may further comprise an insulator plate, wherein the bus bar is seated on a first side of the insulator plate. The bus bar may be seated within a recess provided on the first side of the insulator plate. The insulator plate may include a tab portion corresponding to the tab portion of the bus bar. The tab portion of the insulator plate may be disposed between the fastening block and the tab portion of the bus bar.

[0017] The fastening block may be fabricated from an electrically insulating material. The fastening block may be fabricated from an electrically conducting material, such as a metallic material.

[0018] The fastening block may have at least one threaded insert providing the at least one threaded hole. The at least one threaded insert may be fabricated from an electrically insulating material. The at least one threaded insert may be fabricated from an electrically conducting material, such as a metallic material.

[0019] In accordance with a further aspect of the invention, there is provided the combination as follows: a bus bar for an electrochemical cell stack, the bus bar comprising a main portion that is generally planar and a tab portion having at least one mounting hole; and a fastening block having at least one threaded hole corresponding to the at least one mounting hole of the tab portion.

[0020] In a particular embodiment, the tab portion comprises an angled portion. The at least one mounting hole may be arranged on the angled portion. The angled portion may be generally perpendicular to a general plane of the bus bar.

[0021] The fastening block may be fabricated from an electrically insulating material. The fastening block may be fabricated from an electrically conducting material, such as a metallic material.

[0022] The fastening block may include at least one threaded insert providing the at least one threaded hole. The at least one threaded insert may be fabricated from an electrically insulating material. The at least one threaded insert may be fabricated from an electrically conducting material, such as a metallic material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which show, by way of example, one or more embodiments of the present invention and in which:

[0024] FIG. 1 is a schematic diagram illustrating a fuel cell system where a bus bar assembly according to the present invention may be used;

[0025] FIGS. 2A and 2B are perspective views illustrating the bus bar assembly according to an embodiment of the present invention;

[0026] FIG. 2C is a sectional view illustrating the bus bar assembly shown in FIGS. 2A and 2B;

[0027] FIGS. 3A to 3B are perspective views illustrating the bus bar assembly including a fastening block according to an embodiment of the present invention;

[0028] FIG. 3C is a sectional view illustrating the bus bar assembly shown in FIGS. 3A and 3B;

[0029] FIG. 4 is a perspective view illustrating the bus bar assembly according to the invention as it is mounted on an end plate of an electrochemical cell stack;

[0030] FIG. 5A is a top view illustrating a fastening block according to an embodiment of the present invention;

[0031] FIG. 5B is a section view along line A-A of FIG. 5A;

[0032] FIG. 5C is a section view along line A-A of FIG. 5A, showing an alternative embodiment to what is shown in FIG. 5B; [0033] FIG. 6 is a schematic view illustrating a first embodiment of a bus bar tab according to the present invention; and

[0034] FIG. 7 a schematic view illustrating a second embodiment of a bus bar tab according to the present invention.

DETAILED DESCRIPTION

[0035] Various apparatuses or methods will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover apparatuses or methods that are not described below. The claimed inventions are not limited to apparatuses or methods having all of the features of any one apparatus or method described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or method described below is not an embodiment of any claimed invention. The applicant(s), inventor(s) and/or owner(s) reserve all rights in any invention disclosed in an apparatus or method described below that is not claimed in this document and do not abandon, disclaim or dedicate to the public any such invention by its disclosure in this document.

[0036] FIG. 1, shown is a simplified schematic graph of a Proton

Exchange Membrane (PEM) fuel cell module, simply referred to as fuel cell module 100 hereinafter, that is described herein to illustrate some general considerations relating to the operation of electrochemical cell modules. It is to be understood that the present invention is applicable to various configurations of fuel cell modules that include one or more fuel cells.

[0037] The fuel cell module 100 includes an anode electrode 21 and a cathode electrode 41. The anode electrode 21 includes a gas input port 22 and a gas output port 24. Similarly, the cathode electrode 41 includes a gas input port 42 and a gas output port 44. An electrolyte membrane 30 is arranged between the anode electrode 21 and the cathode electrode 41. [0038] The fuel cell module 100 also includes a first catalyst layer 23 between the anode electrode 21 and the electrolyte membrane 30, and a second catalyst layer 43 between the cathode electrode 41 and the electrolyte membrane 30. In some embodiments the first and second catalyst layers 23, 43 are directly deposited on the anode and cathode electrodes 21 , 41 , respectively.

[0039] A load 115 is connectable between the anode electrode 21 and the cathode electrode 41.

[0040] In operation, hydrogen fuel is introduced into the anode electrode 21 via the gas input port 22 under some predetermined conditions.

Examples of the predetermined conditions include, without limitation, factors such as flow rate, temperature, pressure, relative humidity and a mixture of the hydrogen with other gases. The hydrogen reacts electrochemically according to reaction (1), given above, in the presence of the electrolyte membrane 30 and the first catalyst layer 23.

[0041] The chemical products of reaction (1) are hydrogen ions (i.e. cations) and electrons. The hydrogen ions pass through the electrolyte membrane 30 to the cathode electrode 41 while the electrons are drawn through the load 115. Excess hydrogen (sometimes in combination with other gases and/or fluids) is drawn out through the gas output port 24.

[0042] Simultaneously an oxidant, such as oxygen in the ambient air, is introduced into the cathode electrode 41 via the gas input port 42 under some predetermined conditions. Examples of the predetermined conditions include, without limitation, factors such as flow rate, temperature, pressure, relative humidity and a mixture of the oxidant with other gases. The excess gases, including the excess oxidant and the generated water are drawn out of the cathode electrode 41 through the gas output port 44. As noted previously, in low-pressure fuel cell systems the oxygen is supplied via oxygen carrying ambient air that is urged into the fuel cell stack using air blowers (not shown). [0043] The oxidant reacts electrochemically according to reaction (2), given above, in the presence of the electrolyte membrane 30 and the second catalyst layer 43.

[0044] The chemical product of reaction (2) is water. The electrons and the ionized hydrogen atoms, produced by reaction (1) in the anode electrode 21 , are electrochemically consumed in reaction (2) in the cathode electrode 41. The electrochemical reactions (1) and (2) are complementary to one another and show that for each oxygen molecule (O2) that is electrochemically consumed two hydrogen molecules (H₂) are electrochemically consumed.

[0045] The rate and pressure at which the reactants, hydrogen and oxygen, are delivered into the fuel cell module 100 effects the rate at which the reactions (1) and (2) occur. The reaction rates are also affected by the current demand of the load 115. As the current demand of the load 115 increases, the reactions rate for reactions (1) and (2) increases in an attempt to meet the current demand.

[0046] FIGS. 2A, 2B and 2C show a bus bar 200 having a main portion that is generally planar and an extended tab portion 210. The tab portion 210 has an angled portion 220 that is angled in relation to the main portion of the bus bar 200, with mounting holes 230 arranged on the angled portion 220. The bus bar 200 is shown mounted on an insulator plate 300. The insulator plate 300 is then mounted to an end plate (not shown). The insulator plate 300 may includes a corresponding tab portion 310 for supporting the tab portion 210. With reference to FIGS. 3A, 3B and 3C, a fastening block 240 is arranged to cooperate with the angled portion 220 of the bus bar 200. The fastening block 240 facilitates connection of the bus bar 200 with a contact (not shown). Advantageously, a relatively high torque force can be applied to the fastening block 240 when attaching a contact (not shown), without having to retain the nut portion of a typical nut/bolt fastening arrangement. Tab portion 310 spaces the fastening block 240 apart from the tab portion 210 thereby allowing the fastening block 240 to seat with the angled portion 220 without a bevel edge to account for the rounded inside corner between tab portion 210 and angled portion 220. The fastening block 240 is described in more detail below.

[0047] An alternative to the insulator plate/end plate arrangement is an insulated end plate 400 as shown in FIG. 4. The end plate 400 directly receives the bus bar 200. When using a metallic end plate, and to prevent the outer surfaces of the end plate to be "live" when operating the electrochemical cell, the outer surfaces of the end plate are coated with a coating that is electrically insulating. The bus bar features are identical to what was shown in FIGS. 2 and 3. For both embodiments, the fastening block 240 does not make physical contact with the end plate itself.

[0048] FIGS. 5A to 5C show the fastening block 240 in more detail.

The fastening block has at least one threaded hole 245, one threaded hole 245 for each mounting hole 230 of the angled portion 220 of the bus bar tab 210 (see previous Figures). The fastening block 240 may have at least one threaded insert 250, one insert forming one threaded hole 245. Alternatively, the thread may be formed in the fastening block itself, provided the fastening block material is strong enough to handle the torque from attaching a contact (not shown) to the bus bar tab (210 in previous Figures). FIG. 4B shows the threaded holes 245 as through holes, i.e. the threaded holes 245 run completely through a thickness of the fastening block 240. Alternatively, as is shown in FIG. 4C, the threaded holes 245 may run partly through the thickness of the fastening block 240. It is thus important to position the fastening block with the through holes facing the mounting holes 230 of the bus bar when utilizing this embodiment of a fastening block 240. The fastening block according to the previous embodiment (FIG. 4B) thus has two ways it may be utilized, but is inherently slightly weaker in construction than the embodiment shown in FIG. 4C.

[0049] FIG. 6 shows one embodiment of a bus bar 200 and the extended tab 210' having mounting holes 230. The extended tab 210" in this case has no angled portion (or the angle between the angled portion and the rest of the tab is 180 degrees). The fastening block 240 is thus attached to either side of the tab perpendicularly to a general plane of the bus bar.

[0050] FIG. 7 shows an alternative embodiment to what is shown in FIG. 6, corresponding to what has been shown in FIGS. 2 and 3. The bus bar has an angled portion 220 onto which the fastening block 240 is attached. Advantageously, the fastening block is attached on the angled portion 220 facing the bus bar 200, to facilitate the attachment of a contact (not shown).

[0051] It should be appreciated that the spirit of the present invention is concerned with providing a bus bar for an electrochemical cell system. The present invention is not intended to be limited to only the configurations of the fastening block and tab portion of the bus bar, for example, as shown in FIGS.

6 and 7, and that other possibilities are within the scope of the present invention. For instance, the angled portion 220 need not be exactly perpendicular to or parallel with a general plane of the bus bar 200, with various other angles possible. Furthermore, the type and internal structure of the fuel cell system as described does not affect the design of the present invention. In other words, the present invention is applicable to various types of fuel cells, electrolyzers or other electrochemical cell systems. The position, number, size and pattern of the fuel cell stacks and peripheral devices are not necessarily identical as disclosed herein.

[0052] It is anticipated that those having ordinary skill in this art can make various modification to the embodiment disclosed herein after learning the teaching of the present invention. However, these modifications should be considered to fall under the protection scope of the invention as defined in the following claims.

Claims

CLAIMS:

1. An electrochemical cell stack comprising: a) a bus bar having a main portion that is generally planar and a tab portion, the tab portion having at least one mounting hole; and b) a fastening block having at least one threaded hole corresponding to the at least one mounting hole of the tab portion.

2. The electrochemical cell stack as recited in claim 1 , wherein the tab portion of the bus bar comprises an angled portion, the angled portion provided at an angle to the main portion.

3. The electrochemical cell stack as recited in claim 2, wherein the at least one mounting hole is arranged on the angled portion.

4. The electrochemical cell stack as recited in any one of claims 2 or 3, wherein the angled portion is generally perpendicular to a general plane of the bus bar.

5. The electrochemical cell stack as recited in any one of claims 1 to 4, further comprising an insulator plate, wherein the bus bar is seated on a first side of the insulator plate.

6. The electrochemical cell stack as recited in claim 5, wherein the bus bar is seated within a recess provided on the first side of the insulator plate.

7. The electrochemical cell stack as recited in any one of claims 5 or 6, wherein the insulator plate comprises a tab portion corresponding to at least part of the tab portion of the bus bar.

8. The electrochemical cell stack as recited in claim 7, wherein the tab portion of the insulator plate is disposed between the fastening block and the tab portion of the bus bar.

9. The electrochemical cell stack as recited in any one of claims 1 to 8, wherein the fastening block is fabricated from an electrically insulating material.

10. The electrochemical cell stack as recited in any one of claims 1 to 8, wherein the fastening block is fabricated from an electrically conducting material.

11. The electrochemical cell stack as recited in claim 10, wherein the fastening block is fabricated from a metallic material.

12. The electrochemical cell stack as recited in any one of claims 1 to 11 , wherein the fastening block comprises at least one threaded insert providing the at least one threaded hole.

13. The electrochemical cell stack as recited in claim 12, wherein the at least one threaded insert is fabricated from an electrically insulating material.

14. The electrochemical cell stack as recited in claim 12, wherein the at least one threaded insert is fabricated from an electrically conducting material.

15. The electrochemical cell stack as recited in claim 14, wherein the at least one threaded insert is fabricated from a metallic material.

16. In combination: a) a bus bar for an electrochemical cell stack, the bus bar comprising a main portion that is generally planar and a tab portion having at least one mounting hole; and b) a fastening block having at least one threaded hole corresponding to the at least one mounting hole of the tab portion.

17. The combination as recited in claim 16, wherein the tab portion of the bus bar comprises an angled portion, the angled portion provided at an angle to the main portion.

18. The combination as recited in claim 17, wherein the at least one mounting hole is arranged on the angled portion.

19. The combination as recited in any one of claims 17 or 18, wherein the angled portion is generally perpendicular to a general plane of the bus bar.

20. The combination as recited in any one of claims 16 to 19, wherein the fastening block is fabricated from an electrically insulating material.

21. The combination as recited in any one of claims 16 to 19, wherein the fastening block is fabricated from an electrically conducting material.

22. The combination as recited in claim 21 , wherein the fastening block is fabricated from a metallic material.

23. The combination as recited in any one of claims 16 to 22, wherein the fastening block comprises at least one threaded insert providing the at least one threaded hole.

24. The combination as recited in claim 23, wherein the at least one threaded insert is fabricated from an electrically insulating material.

25. The combination as recited in claim 23, wherein the at least one threaded insert is fabricated from an electrically conducting material.

26. The combination as recited in claim 25, wherein the at least one threaded insert is fabricated from a metallic material.